Difference between revisions of "Boron nitride"

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==Properties==
 
==Properties==
 
===Chemical===
 
===Chemical===
Boron nitride is insoluble in most common acids, but is soluble in alkaline molten salts and nitrides, such as [[Lithium hydroxide|LiOH]], [[Potassium hydroxide|KOH]], [[Sodium hydroxide|NaOH]]-[[Sodium carbonate|Na<sub>2</sub>CO<sub>3</sub>]], [[Sodium nitrate|NaNO<sub>3</sub>]], lithium nitride, magnesium nitride, strontium nitride, barium nitride or Li<sub>3</sub>BN<sub>2</sub>, which are therefore used to etch BN.
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Boron nitride is insoluble in most common acids, but is soluble in alkaline molten salts and nitrides, such as [[Lithium hydroxide|LiOH]], [[Potassium hydroxide|KOH]], [[Sodium hydroxide|NaOH]]-[[Sodium carbonate|Na<sub>2</sub>CO<sub>3</sub>]], [[Sodium nitrate|NaNO<sub>3</sub>]], lithium nitride, magnesium nitride, strontium nitride, barium nitride or Li<sub>3</sub>BN<sub>2</sub>, which are used to etch BN.
  
 
Boron nitride reacts with iodine fluoride in trichlorofluoromethane at −30 °C to produce the  extremely sensitive contact explosive, [[nitrogen triiodide]].
 
Boron nitride reacts with iodine fluoride in trichlorofluoromethane at −30 °C to produce the  extremely sensitive contact explosive, [[nitrogen triiodide]].

Latest revision as of 16:20, 21 March 2020

Boron nitride
Boron nitride bottle.jpg
Boron nitride powder
Names
IUPAC name
Boron nitride
Preferred IUPAC name
Boron nitride
Systematic IUPAC name
Boron nitride
Other names
Azanylidyneborane
Borazon
Elbor
Elboron
Properties
BN
Molar mass 24.82 g/mol
Appearance Colorless crystals
Odor Odorless
Density 2.1 g/cm3 (h-BN)
2.28 g/cm3 (amorph.)
3.45 g/cm3(c-BN)
3.49 g/cm3 (w-BN)
Melting point 2,973 °C (5,383 °F; 3,246 K) (sublimes)
Boiling point 2,973 °C (5,383 °F; 3,246 K) (sublimes)
Insoluble
Solubility Soluble in molten alkali, alkali nitrates and nitrides
Insoluble in organic solvents
Vapor pressure ~0 mmHg
Thermochemistry
14.8 J·K-1·mol-1
-254.4 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich (powder, ~1 μm)
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
2,000 mg/kg (rat, oral)
Related compounds
Related compounds
Aluminium nitride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Boron nitride is a thermally and chemically resistant refractory compound of boron and nitrogen with the chemical formula BN.

Properties

Chemical

Boron nitride is insoluble in most common acids, but is soluble in alkaline molten salts and nitrides, such as LiOH, KOH, NaOH-Na2CO3, NaNO3, lithium nitride, magnesium nitride, strontium nitride, barium nitride or Li3BN2, which are used to etch BN.

Boron nitride reacts with iodine fluoride in trichlorofluoromethane at −30 °C to produce the extremely sensitive contact explosive, nitrogen triiodide.

Physical

Boron nitride exists in multiple forms that differ in the arrangement of the boron and nitrogen atoms, giving rise to varying bulk properties of the material:

  • Amorphous:The amorphous form of boron nitride (a-BN) is non-crystalline, lacking any long-distance regularity in the arrangement of its atoms. It is analogous to amorphous carbon.
  • Hexagonal: corresponding to graphite is the most stable and soft among BN polymorphs; therefore used as a lubricant and an additive to cosmetic products.
  • Cubic (sphalerite structure): variety analogous to diamond is called c-BN; it is softer than diamond, but its thermal and chemical stability is superior.
  • Wurtzite: rarely encountered, is similar to lonsdaleite but slightly softer than the cubic form.

Bulk boron nitride is extremely hard, with the hardness of c-BN being slightly smaller and w-BN even higher than that of diamond. Polycrystalline c-BN with grain sizes on the order of 10 nm is also reported to have Vickers hardness comparable or higher than diamond. Because of much better stability to heat and transition metals, c-BN surpasses diamond in mechanical applications, such as machining steel. The thermal conductivity of BN is among the highest of all electric insulators.

Availability

Boron nitride is sold by chemical suppliers, usually as powder or some other form.

Boron nitride has been identified as the extremely rare mineral qingsongite, which so far has only been found in some minute inclusions within chromite deposits in the Luobusa ophiolite, in Tibet.

Preparation

Hexagonal boron nitride is obtained by the reacting boron trioxide or boric acid with ammonia or urea in a nitrogen atmosphere.

h-BN can be obtained from amorphous BN at high temperatures.

Synthesis of c-BN uses same methods as that of diamond: Cubic boron nitride is produced by treating hexagonal boron nitride at high pressure and temperature, much as synthetic diamond is produced from graphite. Direct conversion of hexagonal boron nitride to the cubic form has been observed at pressures between 5 and 18 GPa and temperatures between 1730 and 3230 °C, that is similar parameters as for direct graphite-diamond conversion.

Wurtzite BN can be obtained via static high-pressure or dynamic shock methods.

Projects

  • Compound collecting
  • Abrasive
  • Crucible
  • Nanoparticles

Handling

Safety

Boron nitride is reported to show weak fibrogenic activity, and to cause pneumoconiosis when inhaled in particulate form.

Storage

In closed bottles or boxes.

Disposal

No special disposal is required. It can be dumped in trash.

Gallery


References

Relevant Sciencemadness threads